Photocatalytic oxidation of benzene to phenol using dioxygen as an oxygen source and water as an electron source in the presence of a cobalt catalyst

Photocatalytic hydroxylation of benzene to phenol by dioxygen (O₂) occurs under visible light irradiation of an O₂-saturated acetonitrile solution containing [RuII(Me₂phen)₃]²⁺ as a photocatalyst, [CoIII(Cp*)(bpy)(H₂O)]²⁺ as an efficient catalyst for both the water oxidation and benzene hydroxylation reactions, and water as an electron source in the presence of Sc(NO₃)₃. The present study reports the first example of photocatalytic hydroxylation of benzene with O₂ and H₂O, both of which are the most green reagents, under visible light irradiation to afford a high turnover number (e.g., >500). Mechanistic studies revealed that the photocatalytic reduction of O₂ to H₂O₂ is the rate-determining step, followed by efficient catalytic hydroxylation of benzene to phenol with H₂O₂, paving a new way for the photocatalytic oxygenation of substrates by O₂ and water.